The verb u"n applies u to each cell as
specified by the rank n .The full form of the
rank used is 3$&.|.n .For example, if n=:2 ,
the three ranks are 2 2 2 ,and
if n=: 2 3,they are 3 2 3 .
A negative rank is complementary: u"(-r) y is equivalent
to u"(0>.(#$y)-r)"_ y .